Photoelectric cell



April 21, 1964 G. A. MORTON PHOTOELECTRIC CELL Filed April 5, 1947 Imnentor Gem'ge A. fllaz'f'ozz M 4% (Ittomeg United States Patent Ofifice 3,130,342 Patented Apr. 21, 1964 3,130,342 PHGTOELECTRIC CELL George A. Morton, Oak Ridge, Tenn, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Army Filed Apr. 5, 1947, Ser. No. 739,717 2 Claims. (Cl. 313103) This invention is an improvement on photoelectric cells having a relatively large electrical output obtained through electron multiplication such as the well known type 931 disclosed in the patent granted June 2, 1942, to Rajchman and Snyder, No. 2,285,126. Photoelectric cells of this type have a relatively small light entrance area and a relatively small active photocathode surface. This limits the conversion of incident light to electrical energy. Caesiated silver is the best photocathode for use in photoelectric cells and since it must be applied inside the evacuated device the dynodes are also of caesiated silver. This is because it is impractical to shield the dynodes from the photocathode in the flashing of the silver and caesium pellets and dynodes of different active material would be contaminated by the silver and caesium vapor. Since the metal vapor in the activation process deposits on the insulation supports of the dynodes and photocathode, detrimental leakage occurs if the voltage between these electrodes is not limited to comparatively low value.

It is an object of this invention to provide a large photosurface area of a photoelectric cell of the 931 type which is not obstructed by a window or other structural member limiting the angle over which the light may reach the photosurface.

Another object is to construct a photoelectric tube so that the photocathode can be sensitized without contaminating the dynodes of the multiplier.

Another object is to widely separate the photocathode or" a photoelectric cell from the multiplying dynodes so that the active surfaces of one may be prepared independently of the other.

Other objects of the invention will appear in the following specification, reference being had to the drawing in which:

The single figure of the drawing illustrates the photoelectric cell of the invention.

Referring to the drawing the part of the evacuated envelope designated 1 houses the photocathode and the accelerating and focusing electrodes while the part 2 houses the multiplier dynodes and collector electrode, the photocathode of the 931 multiplier being omitted. The photocathode 3 may as usual be a film of caesiated silver on the end of the envelope 1. A plurality of accelerating and focusing anodes 4, 5, 6 and 7 are located in the section 1 of the envelope. The supports for these are not shown but they may be of well known form, for example, like that in the application filed jointly by Flory, Ruedy and myself, filed October 5, 1946, Ser. No. 701,588, now Patent No. 2,506,018. Anode 7 has two closely spaced apertured walls 8, 9 with a shutter 10 fiictionally held between them and capable of motion upwards in the figure, so as to close the aperture and prevent silver and caesium from depositing on the dynodes of the multiplier section 2 when silver and caesium material 11 is evaporated in a well known way for forming the photocathode 3. After the metal vapor is deposited the shutter 10 is jarred down to open the aperture for normal use in which position it will remain due to friction.

The electrodes may be of any desired size and the applied voltage may vary but as one example I may say that the electrode 4 may be .25 inch long by 1.3 inch diameter with volts applied. The electrode 5 may be .50 inch long by 1.2 inch diameter with 8 to 13 volts. The electrode 6 may be .875 inch long by 1.1 inch diameter at the large end and .75 inch diameter at the small end with 120 volts. The electrode 7 may be /2 inch long by .75 inch diameter with 800 volts applied. The photocathode is, of course, connected to the negative terminal of the voltage supply. The electrodes may be spaced apart about .125 inch for the dimensions given.

The section 2 of the evacuated envelope contains a screen 12 or equivalent across the aperture of the multiplier which is conductively joined to the first dynode 13. In the multiplier I have provided nine additional dynodes, 14, 15, 16, 17, 18, 19, 20, 21 and 22. A collector 23, such as a screen or grid, is placed inside the C-shaped dynode 22. The operation of the multipliers is the same as disclosed in said Rajchman and Snyder patent except that the photocathode has been displaced by first dynode 13 which may have a voltage, for example, about 50 volts more positive than the anode 7 of the section 2 or negative thereto if it is positive to the photocathode 3. The voltages applied to the other dynodes may progressively increase by an appropriate amount such as 50%, for example, but this may be increased to considerably higher values as silver-magnesium dynodes may be used which may be made outside the tube and later placed therein. These require no subsequent treatment in the tube so that no metal is deposited on the insulation supports to cause leakage. The cross-over point for the elec trons accelerated from the photocathode 3 is made close to the electron lens aperture, normally about one-quarter of an inch but, of course, this may be varied as desired. By varying the potential of the anode 6, the location of the cross-over point may be shifted.

In the operation of the device, a large amount of light is collected by the photocathode 3 augmented by a light collecting lens if desired and a copious supply of photoelectrons is liberated. These are accelerated and concentrated to a narrow beam in front of the multiplier and pass through screen 12 to land on the first dynode 13. The secondary emission ratio of the first dynode may be made greater than in the 931 as greater voltages may be used without leakage along the insulation supports, as no silver or caesium is deposited thereon. The silver and caesium material for vaporization is located in section 1 of the tube and the shutter 16 prevents the vapor from entering the multiplier when they are evaporated by applying voltage to the ends of the conductor on which the material is supported in a known way. The secondary electrons from each dynode bombard secondaries at a greater than unity ratio from the next dynode in succession except those from the dynode 22 until a highly multiplied output is obtained at the collector screen 23.

It will be apparent that a greater or lesser number of accelerating and focusing anodes may be used in the section 1 and that the number of stages of multiplication may be varied as desired.

Various other modifications may be made without departing from the spirit of the invention.

What I claim as new is:

1. A photoelectric cell comprising an envelope including a first tubular portion having a succesively decreasing diameter from one end to the other end thereof, a light transparent plate closing the largest end of said tubular envelope portion, a multiplier dynode electrode mounted within a second portion of said envelope and spaced outside of and beyond the smaller end of said tubular portion and transverse to the axis of said tubular envelope portion, a photocathode film on the inner surface of said transparent plate, a plurality of spaced tubular electrodes coaxially mounted within said tubular envelope portion between said photocathode and said dynode electrode, the tubular electrode closest to said photocathode having a diameter substantially as large as said transparent plate,

said tubular electrode adjacent said dynode having a wall portion substantially closing the passage between said first and second envelope portions.

2. A photoelectric cell comprising an envelope includ ing a first tubular portion having a successively decreasing diameter from one end to the other end thereof, a light transparent plate closing the largest end of said tubular envelope portion, a multiplier dynode electrode mounted within a second portion of said envelope and spaced outside of and beyond the smaller end of said tubular portion and transverse to the axis of said tubular envelope portion, a photocathode film on the inner surface of said transparent plate, a plurality of spaced tubular electrodes coaxially mounted within said tubular envelope portion between said photocathode and said dynode electrode, the tubular electrode closest to said photocathode having a diameter substantially as large as said transparent plate, said tubular electrodes being of successively less diameter with the electrode of least diameter closest to said dynode electrode, whereby said tubular electrodes are adapted to form during tube operation a converging electron lens system for concentrating said photoemission upon said multiplier dynode electrode, said tubular electrode adjacent said dynode having a wall portion substantially closing the passage between said first and second envelope portions.

References Cited in the file of this patent UNITED STATES PATENTS 2,143,582 Schubert et a1. Jan. 10, 1939 2,156,813 Kautz May 2, 1939 2,189,321 Morton Feb. 6, 1940 2,227,031 Schlesinger Dec. 31, 1940 2,231,698 Zworykin et a1. Feb. 11, 1941 2,234,801 Gorlich Mar. 11, 1941 2,239,022 Strubig Apr. 22, 1941 2,285,126 Rajchman et a1. June 2, 1942 

1. A PHOTOELECTRIC CELL COMPRISING AN ENVELOPE INCLUDING A FIRST TUBULAR PORTION HAVING A SUCCESSIVELY DECREASING DIAMETER FROM ONE END TO THE OTHER END THEREOF, A LIGHT TRANSPARENT PLATE CLOSING THE LARGEST END OF SAID TUBULAR ENVELOPE PORTION, A MULTIPLIER DYNODE ELECTRODE MOUNTED WITHIN A SECOND PORTION OF SAID ENVELOPE AND SPACED OUTSIDE OF AND BEYOND THE SMALLER END OF SAID TUBULAR PORTION AND TRANSVERSE TO THE AXIS OF SAID TUBULAR ENVELOPE PORTION, A PHOTOCATHODE FILM ON THE INNER SURFACE OF SAID 